The invention relates to a member for an oil application device which is a component of a fixing device of a capacitance type copying machine, an electrophotographic printer or the like. The invention also relates to a method of manufacturing such a member and to an oil application device.
In a fixing device of a capacitance type copying machine, an electrophotographic printer or the like, during fixation of toner that has been transferred to a recording paper, the toner may adhere to a thermal fixing roller. In order to prevent the toner from soiling another recording paper, a very small amount of releasing oil such as silicon oil is applied to the thermal fixing roll using an oil application device. Thus, toner is prevented from adhering to the thermal fixing roll, and recording papers are prevented from being stuck to one another and rolled up.
Various oil application devices having such a function have already been proposed. For example, Japanese Patent Application Laid-Open No. 2000-079365 discloses an oil application device that is designed such that a felt is wound around and bonded to a peripheral face of a cylindrical porous ceramic compact and that a PTFE film is bonded and fixed to a peripheral face of the felt.
Various methods are adopted to attach the felt layer to the peripheral face of the porous ceramic compact in the above-mentioned oil application device. According to one of such methods, a sheet-like felt fiber is wound around a peripheral face of a porous ceramic compact by one turn, an adhesive is applied to edges of end portions of the felt fiber, and opposed end faces thereof are bonded together and fixed. According to another one of such methods, an adhesive is applied to edges of a felt that has been cut into the shape of a ribbon strip, and the felt is spirally wound around and fixed to a porous ceramic compact while the edges abut on each other without overlapping with each other.
On the other hand, in order to fix a PTFE film to a peripheral face of a felt, it is customary to apply an adhesive to the back of a sheet-like PTFE film and wind the sheet-like PTFE film around a peripheral face of a felt layer so as to fix the sheet-like PTFE film to the felt layer. A method of bonding in this case requires refinements. For instance, an adhesive is applied spirally or in a dotted manner so as to define a section to be bonded and guarantee oil for application of a passage.
However, the oil application device constructed as described above requires separately bonding the felt and the PTFE film and is thus troublesome from the standpoint of processes of fabricating the application device. Further, seam portions of the spirally wound felt is more obstructive to the transfer of oil than the other portions thereof, thus causing a problem of a decrease in amount of application of oil. Such seam portions of the felt exist over the entire peripheral face of the felt layer. Thus, if printing is carried out using this oil application device, streaky irregularities in gloss appear on the entire surface of a printed matter.
On one hand, if the oil application device is used for a certain period, it runs out of oil held therein and requires being replenished with oil. The felt and the PTFE film are damaged after use for a certain period and have no choice but to be destroyed. In particular, the PTFE film is altered by being heated up to 150xc2x0 C. or more at a fixing portion. In addition, the PTFE film suffers a severe deterioration such as deformation or closure of open pore portions resulting from stains of toner components, adhesion of toner components, and heat. It is thus impossible to recycle the PTFE film. Further, the felt layer is also deprived of its flexibility by heat and can no longer guarantee uniform application of a predetermined amount of oil. Therefore, it is difficult to recycle the felt layer as in the case of the PTFE film.
On the other hand, the porous ceramic compact can be recycled if it is impregnated with releasing oil again. However, the recycling of the porous ceramic compact requires peeling off the felt layer and the PTFE film. Even in an attempt to attach a brand-new felt and a brand-new PTFE film, they must be separately bonded with an adhesive as described above. This causes a problem of troublesomeness from the standpoint of processes of reconstructing the oil application device.
It is thus an object of the present invention to provide a member for an oil application device which makes it easy for a porous cylindrical oil retaining member to be covered with, to be fitted with, or to be removed of a member made from a fibrous layer such as a felt or from a porous film such as a PTFE film. It is also an object of the present invention to provide a method of manufacturing such a member and an oil application device employing the member.
The inventors conducted studies wholeheartedly under such circumstances and have discovered the following facts. That is, a sheet-like felt is formed into a tubular object, for example, using a dummy cylindrical mold. A PTFE film is then fixed to a peripheral face of the tubular object with an adhesive or the like, and the tubular object is drawn out of the dummy cylindrical mold, so that a tubular member having a double-layer structure is obtained. A porous cylindrical oil retaining member can be easily covered with, fitted with, and removed of this tubular member. Further, the sheet-like felt is fitted to the dummy cylindrical mold according to a method comprising the steps of folding the sheet-like felt in two, sewing up end portions thereof, cutting off margins of the end portions if need be, reversing the sheet-like felt, and covering the dummy cylindrical mold with it. This method ensures that the sewn-up portions are hidden inside, thus making it possible to stabilize application performance. Finally the inventors succeeded in completing the present invention.
That is, the present invention (1) provides a tubular member for an oil application device which has been formed separately so as to cover a peripheral face of a porous cylindrical oil retaining member, wherein the tubular member for the oil application device has a multi-layer structure including an inner layer and an outermost layer, wherein the inner layer is a fibrous layer, and wherein the outermost layer is a porous film. Adoption of such a construction ensures that the porous cylindrical oil retaining member can be covered with the member for the oil application device easily, thus making it possible to fabricate the oil application device easily and enhance the overall productivity. Further, if the porous cylindrical oil retaining member is recycled, the member for the oil application device can be easily removed from the porous cylindrical oil retaining member, and can be fixed thereto without using an adhesive during assembly. Therefore, the porous cylindrical oil retaining member is prevented from being soiled with an adhesive, and the regeneration cost can be reduced.
Further, the present invention (2) provides the member for the oil application device wherein the fibrous layer is a fiber felt and wherein the porous film is a PTFE film. Adoption of such a construction ensures that the fiber felt can sufficiently perform the function of an oil transfer layer and that the PTFE film can sufficiently perform the function of an oil application amount control layer, thus making it possible to guarantee a fixing roll of uniform application of a predetermined amount of oil without causing irregularities.
Further, the present invention (3) provides the member for the oil application device wherein the fibrous layer and the porous film are bonded together by the mixture of an adhesive and silicon oil. Adoption of such a construction ensures that the adhesive components in their solidified state are dispersed into silicon oil and exist partially inside the open pores in the porous film, thus making it possible to enhance strength and durability of the porous film. On the other hand, since the mixture of the adhesive and silicon oil is microscopically in a state where the adhesive is dispersed into silicon oil, the silicon oil area serves as a passage for releasing oil inside the open pores. Accordingly, the open pores in the porous film are filled with the mixture, whereby releasing oil is guaranteed of a passage despite closure of the open pores. Consequently, it becomes possible to apply a suitable amount of releasing oil and control the amount of application of releasing oil.
Further, the present invention (4) provides a method of manufacturing a member for an oil application device, comprising the steps of winding a sheet-like fibrous material, which is longer than a circumferential length of a dummy cylindrical mold that is substantially equal in diameter to a porous cylindrical oil retaining member to be covered, around the dummy cylindrical mold by one turn so as to form a fibrous layer, sewing up bonded portions, pressing at least the bonded portions so as to form a peripheral face, and winding a sheet-like porous film around the peripheral face of the fibrous layer by one turn so as to bond the sheet-like porous film to the fibrous layer. Adoption of such a construction makes it possible to fabricate the member for the oil application device reliably by a simple method. Further, since the sheet-like fibrous layer is formed into a cylindrical shape, the number of seams in the fibrous layer is reduced. As a result, it becomes possible to achieve uniform application of oil without causing irregularities.
Further, the present invention (5) provides a method of manufacturing a member for an oil application device, comprising the steps of folding a sheet-like fibrous material in two and sewing up end portions thereof, reversing the sheet-like fibrous material that has been sewn up and covering a dummy cylindrical mold, which is substantially equal in diameter to a porous cylindrical oil retaining member to be covered, with the sheet-like fibrous material, and winding a sheet-like porous film around a surface of the sheet-like fibrous material covering the dummy cylindrical mold by one turn so as to bond the sheet-like porous film to the sheet-like fibrous material. Adoption of such a construction makes it possible to fabricate the cylindrical member for the oil application device easily. Also, this construction makes it possible to suppress the influence of the sewn-up portion and to apply oil uniformly without causing irregularities despite the simplicity of processes of fabrication.
Further, the present invention (6) provides an oil application device having a porous cylindrical oil retaining member that is covered on a peripheral face thereof with a tubular member for the oil application device which has been formed separately, wherein the tubular member for the oil application device has a multi-layer structure including an inner layer and an outermost layer, wherein the inner layer is a fibrous layer, and wherein the outermost layer is a porous film. Adoption of such a construction realizes a simple structure in which the porous cylindrical oil retaining member is covered with the tubular member for the oil application device which has been formed separately, thus making it possible to reduce the number of failures and to achieve stable application of oil. Further, if the porous cylindrical oil retaining member is recycled, the tubular member for the oil application device can be easily removed from the porous cylindrical oil retaining member. This makes it possible to enhance the workability during recycling.
Further, the present invention (7) provides the oil application device wherein the tubular member for the oil application device is folded at opposed end portions thereof onto lateral faces of the porous cylindrical oil retaining member and wherein folded portions of the tubular member for the oil application device are pressed and fixed by a fixture member. Adoption of such a construction makes it possible to fix the tubular member for the oil application device to the porous cylindrical oil retaining member without using an adhesive.